The subject matter disclosed herein relates generally to high temperature instrumentation assemblies and, more specifically, to a probe-holding rake structure of machined ceramic material for acquiring measurements in high temperature environments in gas turbine engines and the like.
Instrumentation rake assemblies are used to measure temperatures and pressures in many applications such as within a turbine engine. Typically, instrumentation rakes are configured and positioned to traverse a region of interest, and that region may be in an extremely harsh environment, such as at the exit of a combustor or another location within an engine. To traverse a region of interest, an instrumentation rake assembly may include a number of probes arranged at varying distances along the rake.
Where a probe is intended to measure temperature, the probe may comprise a thermocouple of two dissimilar metals joined at one end. The dissimilar metals of the thermocouple produce a voltage that varies with temperature, and analysis of the voltage can be used to determine sensed temperature. Where the probe is intended to measure pressure, the probe may comprise means such as a tube to enable gas from the sensed region to act upon a strain gage or other apparatus, whereby the apparatus may produce a signal indicative of the sensed pressure.
In both cases, means are necessary for transmitting the signal to a location where it can be recorded and/or analyzed. Where the signal is a voltage, a conductor is necessary to transmit the voltage. Where the signal is a volume of pressurized gas, a tube or other structure is required to enable the pressurized gas (or another intermediate fluid) to act upon the strain gage. Accordingly, instrumentation rake assemblies serve not only to position a number of probes at desired locations within the environment to be sensed, but also to provide means for carrying the signal produced by the probes to one or more locations outside the sensed environment.
While it is often desirable to reduce the impact of an instrumentation rake assembly on the environment intended to be sensed, it is also necessary for the rake assembly to withstand that environment. If that environment is extremely hot, such as in the wake of a combustor or turbine in a gas turbine, the rake assembly must be able to withstand extremely high heat. If that environment entails extreme vibration, high impingement forces, and cyclic variations thereof, a rake assembly must be able to withstand those challenges as well. Otherwise, the rake assembly may fail, causing not only loss of the hosted instrumentation, but also possible damage to downstream components.
Previous attempts to improve the durability of instrumentation rake assemblies in high-temperature environments have employed cooling techniques. Unfortunately, to facilitate cooling of a rake assembly requires cooling passageways within the assembly, thereby increasing the size and complexity of the rake assembly and its disruption of the sensed environment. Moreover, in a gas turbine engine, the pressurized airflow needed to cool a rake assembly in a high-pressure environment, such as in the wake of a combustor or turbine, can be highly parasitic to the thermal efficiency or power output capability of the engine.
Therefore, there is a desire for an instrumentation rake assembly that can enable the instrumentation to withstand increased temperatures and vibrations with reduced cooling and without failure.